As for a method of fabricating a film-like light polarizing device, there have so far been known three kinds of methods. A first method is a method of doping a poly(vinyl alcohol) (PVA) film as drawn with a dichromic dye such as iodine, and so forth, as disclosed in JP-05-019247A {para (0008)}. This is a method whereby a PVA film with a dichromic substance, such as an iodine complex, adsorbed thereto is passed between rotating rollers to undergo uniaxial drawing while being heated, thereby aligning PVA molecules as well as the iodine complex. The film-like light polarizing device of such a makeup as described permits a light component having an oscillation plane orthogonal to a film-drawing direction to pass therethrough, absorbing a light component having an oscillation plane parallel with the film-drawing direction to be thereby lost, so that two sheets of the film-like light polarizing devices superimposed one on another appear black because the light components having all the oscillation planes are absorbed. The light polarizing film fabricated by the first method is inexpensive, and is excellent in light quenching ratio, so that it is in widespread use in the current liquid crystal display device, and so forth, however, the application region thereof is limited to the visible light region.
A second method of fabricating a film-like light polarizing device is a method of dispersing two kinds of polymers or inorganic fine particles into a polymer to be subsequently subjected to uniaxial drawing as disclosed in JP-2002-022966A {Claims, para (0033) to (0043)}. This is, for example, a method of causing respective refractive indexes of mixed substances to coincide with each other in a drawing direction while causing a refractive index difference Δn as large as possible to occur in a direction orthogonal to the drawing direction. In this case, in contrast with the method described, the refractive index difference Δn may be enlarged in the drawing direction while the refractive index difference in the direction orthogonal to the drawing direction may be rendered as Δn=0. In either case, ideally the refractive index difference Δn in one direction is rendered as large as possible, that is, not less than 0.5 while the refractive index difference Δn in the other direction is rendered Δn=0, however, it is extremely difficult to find out such a condition. Accordingly, with the second method of fabricating the light polarizing film, a light polarizing film small in area can be fabricated, but if there occurs a slight difference in localized drawing ratio, a refractive index difference Δn in a portion comes to differ from that in other portions, resulting in weakened light polarizing function. Further, in order to obtain predetermined light polarizing performance, there is the need for increasing the thickness thereof, which makes it difficult to obtain a high-performance light polarizing film small in thickness.
Then, a third method of fabricating a film-like light polarizing device is a method of obtaining polarization property by arranging intervals of fine wires so as to be not more than a wavelength of light to be polarized. A light polarizing film fabricated by this method is called a grid-type light polarizing film exhibiting an action as the light polarizing film if an interval d between the fine wires adjacent to each other is sufficiently shorter than a light wavelength λ, more specifically, if the fine wires are disposed at equal intervals of d<λ/2. The light polarizing film of this type has a function of reflecting a light component having an oscillation plane in the longitudinal direction of metal wires while transmitting a light component having an oscillation plane in a direction orthogonal to the longitudinal direction of the metal wires. Accordingly, the grid-type light polarizing film fabricated by the third method is contrary in operation principle to the film-like light polarizing device fabricated by the first method, and if two sheets of the grid-type light polarizing films are superimposed so as to cross each other at right angles, these act in effect like a mirror because all the components of incident light, having all the oscillation planes, are reflected. With the grid-type light polarizing film, transmittance of light can be enhanced, however, the intervals of electro-conductive fine wires need to be arranged so as to be not more than the wavelength of light to be polarized. Hence, the grid-type light polarizing film has so far been for use in infrared rays and so forth, having a long wavelength, but has seldom been used for visible rays because of difficulty with polarization of the visible rays.
By way of example of the grid-type light polarizing film described as above, in JP-9-090122A {Claims, para (0011) to (0021), FIG. 1}, there is disclosed a method of fabricating a grid-type light polarizing film of a construction where metal is distributed in a grid pattern inside dielectrics, or on the surface thereof, wherein two dielectrics are integrated with each other with the metal in the grid pattern interposed therebetween, and subsequently, the metal in the grid pattern in whole is hot drawn or rolled before fabrication.
However, since the method of fabricating the grid-type light polarizing film, disclosed in JP-9-090122A {Claims, para (0011) to (0021), FIG. 1}, requires heating up to a temperature causing the metal to expand, if a polymer substance is used for the dielectrics, the polymer substance will be in a melt condition or undergo depolymerization at such a temperature, so that it is impossible to fabricate the light polarizing film, and it is difficult to enlarge the area thereof.
Still further, in JP-2001-074935A {claims, para Nos, (0010) to (0014), FIGS. 1 and 2}, there is disclosed a grid-type light polarizing film of a construction comprised of metal portions and dielectric portions, anisotropic in shape, by forming a metal film on a transparent substrate, and drawing the substrate, and the metal film, at a temperature not higher than the melting point of the metal film.
However, with the method of fabricating the grid-type light polarizing film, disclosed in JP-2001-074935A {Claims, para Nos, (0010) to (0014), FIGS. 1 and 2}, as the transparent and soft substrate is uniformly drawn by drawing operation, an uniform drawing force acts on the metal film on top of the substrate, as well, so that metal wires formed of the metal film will not be regularly arranged at intervals on the order of a wavelength of light. More specifically, in the case of using a metal such as gold, excellent in ductility, the metal, together with the substrate, will be extended to thereby keep covering the substrate, and on the other hand, in the case of using a metal such as aluminum, poor in ductility, irregular cracking will occur, or the metal will peel off the substrate, so tat there exists a problem that a polarization effect is hardly obtainable.
Furthermore, as disclosed in JP-2003-529680A (Claims), there has recently been made public a method of fabricating a light polarizing film for a visible light region by forming fine grooves on a glass sheet with the use of a photo resist, and by vapor-depositing a metal thereon, however, with this method, fabrication cost becomes high because of a complex fabrication process involved, and moreover, it is practically impossible to increase an area to 5 cm2 or larger.
Thus, with the above-described methods of fabricating the grid-type light polarizing film, only the grid-type light polarizing film with an area several cm2 at the maximum has been obtained, and it has been impossible to obtain a film-like grid-type light polarizing device with an area larger than the area described as above. Hence, there has been a strong demand for a film-like grid-type light polarizing device large in area, with the polarization effect thereof enhanced ranging from a visible light region to an infrared region, and having a construction where there are alternately disposed electro-conductors, and dielectrics, each having a width on the order of 1/10 of a wavelength in use, that is, in a range of several 10 nm to several μm, and a length not less than 10 times as long as the wavelength in use, that is in a range of several hundred nm to several hundred μm.